Process of drying alkali cellulose



July 5, 1927. 1,635,012

P. C. SEEL PROCESS OF DRYING ALKALI CELLULOSE Filed May 24, 1921 WITNESS INVENTOR Paul afi' eel,

ATTORNEY Patented July 5,1927.

UNITED STATES 1,635,012 PATENT OFFICE.

PAUL C. SEEL, OF ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KODAK COMPANY,

I OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK.

PROCESS OF DRYING ALKALI CELLULOSE.

Application filed May 24, 1921. Serial No. 472,295.

This invention relates to a process for controlling the amount of moisture in alkali cellulose. One object of my invention is to provide a process for removing an excess of water from alkali cellulose speedily and relatively inexpensively and yet without injury to the alkali cellulose. Other objects will hereinafter appear.

In the production of cellulose ethers it has been proposed to incorporate an alkali, like caustic soda, into a mass of cellulose and then treat the mixture with an etherifying agent at increased temperatures and pressures. It has been'found essential that the mixture of the alkali with the cellulose be a eculiarly intimate one. \Vhether the alkali orms a weak chemical combination with the cellulose, whether there is simply a close adsorption of the caustic on the cellulose, or whether there is merely a specially intimate mechanical mixture, it is not necessary to state, but in any event special means have to be taken to insure the proper incorporation of these two ingredients, the product being called alkali cellulose.

One method of incorporation is to dissolve the alkali in an excess of water and then soak the cellulose in the solution for an extended period at the proper temperature. It then becomes necessary to remove the excess of water. In some cases the water may be entirely removed and in others a small amount of it may be retained to modify or assist in the etherifying reaction. It has been found that merely heating the wet alkali cellulose either spoils the latter through an undue attack of the alkali at high temperature, or else is too slow if the temperature be lowered to a safe degree. The use of a vacuum system of drying, of course, causes extended delay unless the temperature be dangerously high.

I have discovered that the excess of water ma be satisfactorily removed from the alkali cellulose by passing into contact therewith a current of relatively dry gas, provided said gas be first made inert to- Ward said alkali cellulose. Small amounts of acid gases, either those that are acid themselves or form acids in contact with moisture, like carbon dioxide, should be substantially removed from the drying stream of gas, because when present they tend to break down the intimate union or mixture of the alkali cellulose, so that upon etherification unetherified fibers or particles remain in the product, and articles made therefrom are not transparent but hazy or cloudy.

In the preferred form of my invention, I circulate a stream -of air successively through a station for removing the acid gases, like carbon dioxide, through a water removing station and then through astation containing the alkali cellulose carrylng an excess of water. In certain forms of my invention the elimination of the acid material from the drying gas may take place either before or after the lowering of the water vapor content of the gas.

In the accompanying drawing the single figure is a diagrammatic side elevation, partly in section, illustrating one apparatus for carrying out my process.

One is a container carrying a series of shelves 2 which may be of foraminous structure to carry the wet alkali cellulose. These shelves are either removable from the 'container or readily accessible from the exterior of the chamber in any well known way. At the top of the container there is a pipe 3 connecting by extensions 4 with a gas blower or pump 5 which in turn is connected by pipe 6 with absorption chamber 7 The latter has perforated or foraminous shelves 33 carrying any suitable absorbing material for acid gases, such, for instance, as calcium or sodium hydroxid. The con tainer 7 is connected by pipe 9 to the bottom of tower 10 in which is a set of open refractory brick Work 11 over which a desiccating liquid may pass from pipe 12 and distributor 13. The liquid collects on the inclined bottom 14 and drains into pipe 15 from whence it is circulated upward in pipe 12 by pump 16. I may use, for instance, concentrated sulfuric acid as the waterabsorbing material.

Abovev the tower 10 is a baflie and absorption box 17 containing bafiles 18 to catch any spray or suspended particles of acid in the ascending stream of gas. As an added precaution, I provide perforated shelves 19 carrying activated carbon or caustic, or other suitable material for ab sorbing any acid particles or fumes that may pass the baffles 18.

Connected with the box 17 is a refrigeration chamber 20 carrying cooling coils 21 in which brine or other refrigerating liquid is circulated in the customary manner. A pipe 22 connects chamber with a series of convolutions 23 which are surrounded by a heating chamber 24. through which is circulated warm water, warm air or steam, pipe being an inlet and pipe 26 an outlet. All of the pipes and connections shown in the figure may be provided with controlling valves, as will be understood by persons 'skilled .in this art, these features bein'g omitted from the diagram for the sake of clearness.

The alkali cellulose containing the excess of moisture having been charged into shelves 2 of container 1 in layers of suitable thinness, a current of inert drying gas is forced through them. For cheapness, I use ordinary air, but nitrogen or other suitable gas which is inert by itself may be used. By inert I mean that it does not break down the intimate commingling of the alkali and cellulose to such an extent that the final ethers are impaired. The dry gas, which takes up moisture from the alkali cellulose, passes through pipe 3 and extensions 4 to the pump or blower 5, which then forces the stream through the pipe 6 and. through the caustic tower 7 where any carbon dioxide or other acid gases (which might be presentin the neighborhood of chemical plants) are absorbed. The gas being harmless by itself and being freed from noxious gases thus becomes inert.

It passes through pipe 9 and thence upward through the checker work 11, where it meets a stream of concentrated sulfuric acid that absorbs moisture from it. Rising through the box 17 any particles of acid trapped in the stream of gas are removed by bailles 1 while any fumes or acid vapors are absorbed by the material on shelves 19. \Vhcn the gas or air reaches the refrigerating chalnber 20, it is chilled by the coils 21 to such an extent that part of the moisture, not previously removed, is condensed and passes out through any suitably trapped drain 27.

The gas having thus become both inert and very low in its water content'is then warmed in the convolutions 23 but only to used alone.

a point below the decomposition temperature of the alkali cellulose,-that is, the tempera ture at which the cellulose is injuriously attacked by the alkali.

The stream of drying air or gas is repeatedly circulated through the apparatus, the above described operations being successively performed until the water content of the alkali cellulose reaches the desired amount. This can be determined by removmg and testing samples if necessary.

While I have indicated both a sulfuric acid tower and a refrigerating chamber in series, as devices for drying the air or gas, nevertheless, either of these agencies may be For example, I may shut off the sulfuric acid in the tower 10 and use the refrigerating chamber 20 as the sole desiccating means. Or I may shut off the supply of cooling fluid from coils 21 and omit the heating fluid from the chamber 24. Then the absorption of moisture from the circulating stream of gas will take place entirely in the tower 10.

The alkali cellulose may be formed by soaking the cellulose in an excess of both alkali and water. The cellulose is then wrung or pressed to mechanically remove some of the liquid. Then it is dried by my process as above described.

Having thus described my invention, what I claim as new and desire to secure by Let ters Patent is:

l. The process of drying alkali cellulose for making haze-free cellulose ether containing an excess of water, which comprises the steps of lowering the water vapor in air containing carbon dioxide, removing said carbon dioxide and then passing said air into contact with said alkali cellulose.

2. The process of drying wet alkali cellulose for making haze-tree cellulose ether to control the water content thereof, which comprises repeatedly circulating a stream of air through an absorbent of carbon dioxide and through said alkali cellulose, water vapor being removed from the air during each cycle by cooling and warming the air.

Signed at Rochester, New York, this l l-th day of May, 1921.

PAUL C. SEEL. 

